1. Field of the Invention
The present invention relates to detection technologies for gunpowder-kind materials such as explosive substances, dangerous objects such as flammable substances, poisonous gases, and legally prohibited medications such as drugs (all of which, hereinafter, will be generically referred to as “special drugs” for convenience). More particularly, it relates to a detection method and its device that, by using a mass spectrometer, detect whether or not a special drug is present inside, e.g., baggage such as a piece of hand baggage, freight, and a suspicious object.
2. Description of the Related Art
Generally speaking, in such locations as an airport and an event grounds where a large number of people come and gather, a detection device has become necessary which is designed for detecting special drugs such as an explosive substance. This detection device is requested for implementing the safety of passengers and event participants, or the maintenance of public peace and order there. Moreover, a request for a detection device has been also made for checking a suspicious object in, e.g., a mail, a home-delivered parcel, and a rental safe-deposit box of a bank. As one of the detection devices of this kind, a hand-baggage checking device using an X-ray transmittance device, a metal detector, or the like has been widely used with airports as its center. Here, the X-ray detection device or the like is based on a detection scheme referred to as “bulk detection”. In the bulk detection, a special drug to be detected as a target is recognized as a piece of lump, then judging the presence based on information about its configuration or the like. Also, a detection method on the basis of gas analyses is referred to as “trace detection”, where a substance is identified from the chemical analysis information. The trace detection exhibits a characteristic of making it possible to detect the extremely small amounts of components adhering to a bag or the like. In particular, in accompaniment with a tendency to seek security enhancements socially, a device is now desired which, by a combination of the bulk detection and the trace detection, allows a dangerous object to be detected with a higher accuracy.
Meanwhile, in order to find out legally prohibited drugs brought in via various routes, the detection device is also used at a customhouse or the like. Although, at the customhouse, the bulk detection device and drug detection dogs are mainly used, it is now being requested to implement a trace analysis device designed for the legally prohibited drugs in substitution for the drug detection dogs. In the trace detection, the various analysis methods, such as the ion mobility spectroscopy and the gas chromatography, are being attempted. In addition, the development and research of a device which simultaneously exhibits all of the following characteristics is now being promoted: The detection speed and sensitivity to be requested as the detection device, and the selectivity of making it possible to detect a specific substance in a selective manner.
In the situation like this, since, basically, the mass spectroscopy is superior in the detection speed, the sensitivity, and the selectivity, a detection technology on the basis of the mass spectroscopy has been proposed (refer to JP-A-7-134970). According to this technology, the presence or absence of a special drug is judged as follows: A sample gas is absorbed by an absorption probe, thereby being guided into an ion-source so as to be ionized. Next, the ions of the sample gas containing drugs are converged by being passed through an electrostatic lens or the like, then being guided into a detector to measure the mass spectrums of the sample gas. Moreover, based on this measurement result, a data processing unit including a computer or the like identifies one or plural m/z (i.e., ion mass-number/ion charge-number) value or values indicating a special drug or drugs, thereby creating the mass spectrum or spectrums. Furthermore, the presence or absence of the special drug is judged based on this mass spectrum, and also its type is identified at the same time. Finally, if the special drug has been detected, an alarm or the like is outputted to be displayed.
However, here, there exists a case where a chemical substance, from which ions having the same m/z value as that of ions generated from a special drug will be generated, is present in the sample gas. In this case, there exists a possibility of issuing a false report, i.e., the alarm is displayed despite the fact that no special drug is present. For example, there has existed a possibility that, at the time of detecting a stimulant inside a piece of hand baggage, a false report is issued in reaction to a component of cosmetics put inside the hand baggage. This phenomenon, which is attributed to the low selectivity of a mass analysis unit for analyzing ions, is caused by its inability to distinguish between ions resulting from the stimulant and ions resulting from the cosmetics both of which have the same m/z value by chance.
As a method of enhancing the selectivity in the mass analysis like this, the tandem mass spectroscopy has been proposed. In the tandem mass spectroscopy, the mass analysis is performed at two stages, using a triplet quadrupole mass spectrometer or a quadrupole ion-trap mass spectrometer. Namely, in the mass analysis at a first stage, the m/z values of the ions generated at the ion-source are measured. Next, from among the ions having the various m/z values, ions having a specific m/z value are selected. Moreover, the selected ions (i.e., precursor ions) are dissociated by the collision with a neutral gas or the like, thereby generating decomposition ions (i.e., fragment ions). Furthermore, in the mass analysis at a second stage, the mass analysis of the fragment ions is performed. In the tandem mass spectroscopy like this, when any one of the precursor ions is dissociated, which of the sections within its molecule will be cut off depends on the chemical-bond strength on each section basis. Consequently, analyzing the fragment ions allows the acquisition of the mass spectrums which include exceedingly ample information about the molecular structures of the precursor ions. As a result, even if the m/z values of the ions generated at the ion-source are identical to each other by chance, by checking the mass spectrums of the fragment ions, it becomes possible to judge whether or not the special drug to be detected is contained in the sample gas.
The tandem mass spectroscopy, however, necessitates a longer checking time as compared with the normal mass spectroscopy. This condition results in, e.g., an undesirable possibility of causing a traffic congestion of plural pieces of hand baggage flowing on board a hand-baggage transportation bench. Accordingly, in order to shorten the checking time needed for the tandem mass spectroscopy, the following proposal has been made (refer to W0-02/25265A1): Namely, only when the precursor ions resulting from the special drug have been detected in the mass analysis at the first stage, the mass analysis at the second stage is executed. This proposal is based on an assumption that no special drug is contained in almost all the pieces of hand baggage.
In this way, it is possible to shorten the time needed for the mass analysis of the special drug. Nevertheless, this checking method still necessitates too much time because of its checking way, i.e., in the hand-baggage checking or the like, trouble is taken to open suitcases, briefcases, bags, parcels, and the like one by one, and the air around goods stored inside the hand baggage is absorbed. Accordingly, the following attempt has been made (refer to JP-A-7-134970): Namely, the sample gas leaking from a piece of hand baggage or the like is absorbed by the absorption probe or the like, thereby being introduced into the mass spectrometer via a pipe path such as a hose. However, there exist occasions where, depending on the type and packing style of the special drug, the special drug leaking from the baggage or the like is too small in amount, or the special drug is the type of special drug that is difficult to become the gas (i.e., vapors) at the room temperature. On these occasions, merely absorbing the air on the surface of the check target by the absorption probe, in some cases, gives rise to a problem that the sample gas introduced into the mass spectrometer is insufficient in amount or concentration. Also, if the check target on the check bench and the mass spectrometer are positioned with a considerable distance apart, it takes the sample gas a time to reach the ion-source via the pipe path such as the hose. This results in a problem that the detection speed is lowered.
As a countermeasure hereto, conventionally, portable-type sample pick-up devices have been proposed (refer to JP-A-5-332894 and JP-A-2-296128). The sample pick-up device disclosed in JP-A-5-332894 is as follows: A sample-collecting filter is inserted into a casing with a built-in absorption fan such that the sample-collecting filter is in an attachment/detachment-capable manner into/from the front-end portion of an absorption pipe. This configuration collects environmental-pollution substances and dangerous objects existing in the air. Also, according to JP-A-2-296128, the sample pick-up device heats the surface of the check target to vaporize substances adhering to the surface. Simultaneously, the device intermittently injects an air-jet to promote the removal of the substances adhering to the surface, then absorbing the vaporized sample from the aperture of a nozzle so as to capture the sample into a collector. This collector, which includes a metallic ribbon wound in a coil-shaped manner inside a cylinder-shaped housing, allows the sample gas to be captured on the surface of the metallic ribbon by adsorption or the like. Concerning the sample captured into the collector, after the nozzle of the sample pick-up device has been connected to a sample absorption opening of the mass spectrometer, the collector is heated so as to detach the adsorbed sample. This makes it possible to introduce the sufficient amount and concentration of sample gas into the mass spectrometer.
By the way, the portable-type sample pick-up devices disclosed in JP-A-5-332894 and JP-A-2-296128 allow the detection by the mass spectrometer to be easily performed even if the check target is a freight container, a vehicle, or the like which is located outdoors.
Nevertheless, the sample pick-up device disclosed in JP-A-5-332894 has the following problem: Namely, on the occasions where the special drug leaking from the baggage or the like is too small in amount, or the special drug is the type of special drug that is difficult to become the gas (i.e., vapors) at the room temperature, merely absorbing the air on the surface of the check target by the absorption fan, in some cases, gives rise to a problem that the picked-up sample is insufficient in amount or concentration. Meanwhile, the sample pick-up device disclosed in JP-A-2-296128 has the following problem: Namely, if, when performing the checking continuously, a sample at a preceding checking remains on the collector without being fully vaporized, the reliability of the subsequent checking is lowered. This is because the collector for capturing the sample is integrally molded with the main body of the pick-up device. When trying to solve the problem like this, treatments such as washing the collector and its periphery must be performed. This results in a problem that the checking speed cannot be increased. Also, if there exist the large number of check targets, the sample pick-up devices corresponding to the number of the check targets must be prepared, which is inconvenient.